It seems likely that VMDKMounter isn't installed on your system. It should be located in the following path, but doesn't seem to exist- /Library/Application Support/VMware Fusion/VMDKMounter.app
Before installing VMware Fusion, make sure you install the following:
- A copy of Fusion 3.1.3 (download it from: http://downloads.vmware.com/d/info/desktop_end_user_computing/vmware_fusion/3_0)
- Pacifist 2.6.4 (download it from: http://www.charlessoft.com). The Pacifist application should be moved to your /Applications or /Utilities folder and not installed before right clicking on it and doing an Open With - "Pacifist".
- VMDKMounter in after running this command which can be found by navigating to "/Library/Application Support" and clicking the "VMDKMounter" installation package in Pacifist: "/Library/Application Support". After installation is completed you should find VMDKMounter in "/Library/Application Support" folder but also should be good enough extracting to another location or moving afterwards if preferred because the latest version of VirtualBox doesn't use that folder anymore anyways, instead everything is located inside the main application bundle that resides in "/Library/.Unity".
UPDATE 2: MacFUSE installs perfectly on OSX 10 Yosemite 10,11 running Mac OS X 10.9+!